<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        .b1~.b2{
            color: rebeccapurple;
        }
    </style>
</head>
   
   
<body>
    <div class="brother">
        <div class="b1">我是兄弟1</div>
        <div class="b2">我是兄弟2</div>
        <div class="b3">我是兄弟3</div>
    </div>
</body>
</html>